1. Field of the Invention
This invention relates generally to vision correction by spectacles and eyeglasses and more specifically to eye contact type opthalmic lenses.
2. Description of the Prior Art
Contact lenses are well known in the art and have enjoyed commercial success for some time. Early disclosures of contact lenses are typified by U.S. Pat. Nos. 722,059 to Volle and 1,869,366 to Dallos which describe scleral lenses made of glass. U.S. Pat. Nos. Re. 25,286 and Re. 29,229 are exemplary of disclosures relating to corneal contact lenses.
Much effort has been directed to improving the shape and design of the interior surface of contact lenses. Improved interior surface designs are generally directed to such advantages as increased comfort, improved tear exchange and the like.
For example, Fertsch et al. disclose in U.S. Pat. No. 1,921,972 a scleral lens having its inner surface formed from two spherical sections, each section having a different radius of curvature and spherical center. The shape edge where the two sections meet is smoothed by forming a third spherical cut. Discomfort to the eye caused by the sharp edge is thus reduced.
In U.S. Pat. No. 3,187,338 to Neefe, a corneal contact lens which has an aspherical inner surface is disclosed. The inner surface of the Neefe lens defines a sine curve so that its central area has a radius of curvature shorter than the cornea to be fitted and the outer edge has a longer radius. The lens of Neefe contacts the cornea in a load-bearing ring around its shoulder, leaving a vault over the center of the cornea. The position of the load-bearing ring on the cornea shoulder varies as the shape of the cornea changes. The edge of the lens is spaced apart from the cornea.
U.S. Pat. No. 3,495,899 to Biri shows yet another design for the inner surface of a contact lens. The inner surface of the scleral lens disclosed by Biri has a central corneal section and two concentric peripheral sections. The first peripheral section has a radius of curvature with its center on the optical axis through the corneal zone. The second peripheral zone has its center of curvature displaced to the nasal side of the optical axis. The second peripheral zone is thus flatter on the nasal side to more closely approximate the shape of the eye during close reading.
The invention described in commonly assigned copending patent application U.S. Ser. No. 919,651, filed June 28, 1978, relates to a semi-scleral contact lens having an inner surface shaped relative to the topography of an individual eyeball so as to provide improve centering of the lens, central and edge contact between the lens and the eye with tearfilm clearance there between and tear exchange with blinking. This lens has a central spherical optical zone which is the spherical equivalent of the radius of curvature of the cornea at its optical center line and the corneal dimensional diameter. The lens also has a curved peripheral section and a conical section between the peripheral section and the optical zone. The conical section is tangent to the optical zone and to the peripheral zone at their edges.
Girard et al. (U.S. Pat. No. Re. 29,229) shows semi-scleral contact lenses which arch over the cornea and also lenses which are flush fitting and in total contact with the cornea.
Scleral lenses (such as those disclosed by Volle and Dallos) have not been in popular use recently. Their design does not normally allow for movement of the lens on the eye, and it is known that such movement is desirable. When scleral lenses are made from an oxygen impermeable material, the supply of oxygen to a large area of the eye is blocked.
Semi-scleral and corneal contact lenses have been growing in popular use in recent years. However, an entirely satisfactory design for the inner surface of the lens has not been found.
Continuing research and development efforts have been directed to overcoming the disadvantages of current designs. For example, the corneal lens of Neefe demonstrates a less than ideal tear exchange upon blinking. Tear exchange is inhibited by the load-bearing ring. Another disadvantage of the Neefe design is that the raised edges of the lens can be an irritant to the inside of the eyelid.
Lenses designed to provide a vault over the cornea and lenses which fit flush with the cornea (such as the Girard et al. lenses) frequently result in less than desirable tear exchange upon blinking. Uninhibited tear exchange is desirable so as to provide the cornea with a constantly renewed supply of freshly oxygenated tears.
The design disclosed in copending application U.S. Ser. No. 919,651, filed June 28, 1978, shows improved centering of the lens, improved tear exchange and avoids the problem of eyelid irritation. However, even greater tearfilm clearance and tear exchange is desirable.
Extensive activity in contact lens development has resulted in lenses formed from a variety of materials having different properties. Materials used for contact lenses include plastics, such as polymethylmethacrylate; hydrogels, such as hydroxyethylmethacrylate; and rubbers, such as silicone rubber. A single lens design which can be used with a wide variety of these materials is desirable.